In the fetal heart, there is a small communication, referred to as the foramen ovale, in the septum between the right and left atria. In the unborn fetus, this communication allows blood to bypass the lungs. Fetal blood is oxygenated by the lungs of the mother. This communication normally closes within the first year after birth, and oxygenation is carried out through the baby's own lungs. Although the remnant of the opening remains in the septum after birth, the remnant normally does not allow passage of blood.
In some cases, however, this opening (the foramen ovale) remains patent and the baby's oxygenated blood is diluted by un-oxygenated venous blood. Babies with this condition often have very little energy, are cyanotic (blue coloration), and do not progress well after birth. In order to repair this defect, the opening can be closed by surgical methods, or by newer percutaneous methods. This condition in newborns is often referred to as an atrial septal defect (ASD).
In recent years, physicians have also discovered that in a large percentage of adults, estimated at about 30%, the foramen ovale has not completely sealed, and remains as a small patent foramen ovale. In these adults, there is still some leakage across the septum through the remnant foramen ovale. Although such leakage is not always problematic, the leakage can be aggravated upon certain types of strain or valsalva. Intermittent leakage of blood through the PFO has been linked to migraine headaches and other maladies. In addition, a PFO is suspected as being a passageway for blood clots. Passage of clots through the opening can lead to a stroke or a transient ischemic attack (TIA).
The leaking, or patent, foramen ovale does not result from the same physiological structure as an ASD. An ASD is normally a definable hole that extends through the septum. Such holes can be occluded by passing known occluder devices through the hole, such that the devices anchor on each side of the septum to form a seal. Current devices that are commonly used for ASD repair include the Amplatzer ASD Occluder, available from AGA Medical, and the Gianturco occluder coils, available from Cook Incorporated.
Unlike the definable hole that forms an ASD, the foramen ovale is a small channel or slot-type structure that is defined by the septum and a flap that covers a part of the ovale. With a PFO, the septum and the flap normally overlap to a certain degree, and are not fused together as in the normal case. As a result, small amounts of blood may leak through a passageway that extends between the septum and the flap.
Currently available ASD repair devices are ill suited for repair of a PFO. As stated, ASD repair devices normally comprise an occluder-type structure that is extended through the septum hole that comprises the defect to seal the opening. However, with a PFO, the openings on each side of the septum are offset, and not in line with each other (i.e., not directly across from each other). The leakage path is under a flap, and through a narrow passageway, rather than a defined hole. Thus, it is not generally sufficient to merely provide a plug for a hole, as in conventional ASD repair.
Open heart surgical methods have been used for PFO repair. Such methods normally entail breaking open the chest cavity, and cutting into the heart muscle. The flap is then sutured or otherwise attached to the septum, in a manner such that the passageway is closed. Although generally effective for closing the PFO, such methods are intrusive, costly, and require an extended recovery period for the patient.
Recently, percutaneous methods have been developed for repair of a PFO. These methods involve utilizing conventional percutaneous entry techniques, such as the Seldinger technique, and passing a catheter through a vessel into the right atrium of the heart. One device used in such methods, known as the Amplatzer PFO Occluder, comprises a plug-like device formed of a self-expanding wire-mesh with double discs. This device contains inner polyester fabric patches that, along with the wire mesh, are intended to cause the formation and accumulation of a blood clot. The resulting blood clot is positioned to block the opening. Devices of this type are complex mechanically, require a high level of skill to insert properly, and result in the formation of a clot which actually forms the seal.
There exists a need for a device for providing effective closure of a patent foramen ovale, which device is suitable for percutaneous entry, is less complex mechanically and operationally when compared to prior art devices, and can be utilized for patent foramen ovale closure with minimal trauma to the patient.